Historical:Brandon Bridge Member
H. B. Willman and Elwood Atherton
The Brandon Bridge Member of the Joliet Formation (Willman, 1973, p. 20) is named for Brandon Bridge over the Des Plaines River on the southwest side of Joliet, Will County.
The type section of the Brandon Bridge Member is in the Lincoln Stone Company quarry southwest of the bridge (S1/2 SE 20 and N1/2 NE 29, 35N-10E).
Extent and Thickness
The Brandon Bridge Member is 29 feet thick at the type locality, but thins southward and is only 10.5 feet thick where exposed along the Kankakee River east of the Warner Bridge in Kankakee County (NW SE SW 31, 12N-11E).
The Brandon Bridge Member of the Joliet Formation (Willman, 1973, p. 20) is the basal member.
In the Joliet area the Brandon Bridge Member is differentiated into two parts by a bed of green to black shale as much as a foot thick, but generally only an inch or two thick. The lower part is the more shaly and contains beds of red crinoidal dolomite interbedded with very argillaceous gray and red dolomite. The upper part is less shaly and most of ii is gray, mottled with red and green. The top is placed at the highest strong shaly parting.
The abundance of arenaceous Foraminifera in the member has been noted, and Bumastus (fig. S-12) is locally present, particularly in the middle shale.
WILLMAN, H. B., 1973, Rock stratigraphy of the Silurian System in northeastern and northwestern Illinois: Illinois State Geological Survey Circular 479, 55 p.
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